France's interior minister called for a nationwide legal clampdown on UberPOP on Thursday, siding with taxi drivers who blockaded major transport hubs in angry protests against the U.S. online ridesharing service.

Arguing that the service represented unfair competition, cabbies blocked roads to the French capital's Charles de Gaulle (CDG) and Orly airports, prompting operator Aeroports de Paris to warn travelers to use local train services.

"Access by road is completely blocked," the company said on its website. "The only way to get to CDG is [by train]."

It was the second wave of transport disruption in France in a week after Monday's strike by ferry workers at the northern port of Calais created a 10-kilometer (6-mile) tailback.

Migrants camping around the city tried to board trucks in an attempt to stow away on Channel Tunnel trains going to Britain.

At Charles de Gaulle airport on Wednesday, staff advised passengers to avoid the traffic chaos by walking between terminals. Dozens of passengers lined the roads, with some scrambling up slopes and across motorway barriers, a Reuters witness said.

Elsewhere, French TV showed images of burning tires blocking part of the ring road around Paris, overturned vehicles, and scuffles between cabbies and other drivers. Police in riot gear at one point intervened using tear gas.

Cabbies set up barriers around Marseilles and Aix-en-Provence in southeast France, including at motorway exits, and blocked access to train stations in the two cities.

"We are faced with permanent provocation [from Uber] to which there can only be one response: total firmness in the systematic seizure of offending vehicles," G7 taxi firm head Serge Metz told BFM TV.

'Safer in Baghdad?'

Among travelers caught up in the chaos was U.S. rock singer Courtney Love, widow of late Nirvana lead singer Kurt Cobain, who wrote in a Tweet appeal to the French president that her car had come under siege by protesting taxi drivers.

"Is it legal for your people to attack visitors? Get your ass to the airport ... this is France?? I'm safer in Baghdad."

It was not immediately possible to verify that incident.

However, the protests were among the fiercest in a series of strikes and other demonstrations across Europe against the San Francisco-based company, whose backers including investment bank Goldman Sachs and technology giant Google. It is valued in excess of $40 billion.

In a toughening of the French stance, Interior Minister Bernard Cazeneuve ordered Paris police to issue a decree banning the activity of UberPOP, "given the serious public order disturbances and development of this illegal activity."

He also ordered local police chiefs and prosecutors to clamp down on what he said was a failure by Uber to pay social and tax charges in France.

Uber spokesman Thomas Meister accused Cazeneuve of over-riding the normal legal process. "The way things work in a state of law is that it's for the justice to judge whether something is legal or illegal," he said.

Uber, which says it has one million users in France, links drivers to passengers via a smartphone app and has expanded its UberPOP service in French cities, provoking anger from taxi drivers who see it as unfair competition. UberPOP links drivers of private cars with potential passengers at cheaper rates than traditional cabs.

A law from October 2014 placed a ban on putting clients in touch with unregistered drivers. Uber has contested the rule, saying it is unclear and counter to the freedom to do business.

Meister said he expected the Constitutional Council to give its view on the law in the next three months, adding that Uber considered part of it to be unconstitutional.